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Intermediate 1
Physics
Movement

Forces

Speed and acceleration

Moving bodies
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Intermediate 1
Physics
Movement

Forces
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Measuring force
Forces can be measured using a n e
_w
_ t_ o_n_
balance.
When a force acts on a spring balance, the
spring inside it s _
t _r _
e _t _
c _h _e _s .
The position of the stretched spring on the
s_
c _a _l _
e tells you the size of the force.
ew
t _
o_
n , symbol N.
The unit of force is the n _
__
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Weight
A newton balance is used to measure
f _o _
r c_ _
e.
_
_ newtons
10
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Weight
Weight is a f _o _
r c_ _
e.
Weight is the pull of the Earth on an
object due to g _r _a _
v _i _t _
y.
A 1 kilogram mass (1 kg) has a w e_ _i _g _
h t_
of 10 newtons (10 N).
This means the earth p _
u _l _l _
s the
1 kilogram mass with a force of 10 newtons.
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Calculating weight
For any object we can find its weight if
we know the mass of the object in
kilograms.
weight = 10 x mass
newtons (N)
kilograms (kg)
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Calculating weight
example 1:
Find the weight of a 2 kg bag of sugar.
weight = 10 x mass
= 10 x 2
= 20 N
The weight of a 2 kg bag of sugar is 20 N
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Calculating weight
example 2:
Find the weight of a 55 kg pupil.
weight = 10 x mass
= 10 x 55
= 550 N
The weight of a 55 kg pupil is 550 N
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Friction
o _t _i _
o n_
Friction is a force that opposes the m _
of a body.
t o_ p_ a moving
The force of friction can s _
l o_w_ it down.
object or s _
The force of friction can also keep objects from
o v_ e_ .
starting to m _
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Friction
F_
r i_c_t _i o_ n_ _ is caused by the contact of two
surfaces.
If objects do not slide across each other easily,
the force of friction between the surfaces of
a r_ g_e_ .
two objects is l _
If the objects slide e a
_ s_ i_l y_ _ , the force of
friction is small.
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Friction
When the force of friction between surfaces is
h_
i g_h_ , we say they are rough, when the force
m _o _
o t_ h_ .
of friction is low, we say they are s _
H i_g_h_ Friction
Sliding rough surfaces is like
sliding the bristles of two
brushes - it is difficult.
Lo
_w
_ Friction
Sliding smooth surfaces is
like sliding the backs of two
brushes - it is easy.
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Changing Friction
The force of friction can be increased by making the
surfaces r o
_ u_ g_h_e_r_ or by pressing the surfaces
a r_ d_ e_r_ together.
h_
The force of friction can be reduced by making the
o t_ h_ e_r_ or lifting the surfaces away
surfaces s m
_ _o _
from each other.
Lubrication for example, uses o i_l _ which lifts two
surfaces apart and r e
_d
_ u_ c_e_s_ the force of friction.
Air can also be used to lift surfaces apart
o v_ e_r_c_r _a _f _
t _.
e.g. in the h _
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Streamlining
When an object moves through the air, the air rubs
against the object causing friction; this air friction is
e s_ i_s _t _
a n_ c_ e_ _ .
called air r _
Streamlining is when you change the shape of the object
ed
to r _
_ u_ c_e_ the air resistance.
The lines in wind tunnel tests
show the pattern of a i_r_ flow.
The smoother the air flow, the
l_
e s_ s_ the air resistance.
The shape with the least air resistance is the
o s_ t_ streamlined.
teardrop shape - this is the m _
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Cars and Streamlining
W i_n_d_ tunnels are used to improve the streamlining of
cars.
The shape of a car can be made like a teardrop or like an
aeroplane wing to r e
_ d_ u_ c_e_ air resistance.
Sometimes a spoiler is fitted at the back to improve the
air f l_o_w_ making it more streamlined.
Another way to reduce air resistance is to make the car
r o_ u_n_d_ .
closer to the g _
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Balanced Forces
When two forces are the same size as each other and
act on the same object but in opposite directions, they
balance each other. The forces are called balanced
forces.
Some examples of balanced forces are;
20 N
F
20 N
F
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Balanced Forces
Some examples of balanced forces are;
15 N
F
30 N
F
F
30 N
F
15 N
All of the objects shown above are acted on by
b_
a l_a_n_c _e _
d _ forces.
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Examples of balanced forces
When two tug-of-war
teams are pulling against
each other but neither is
making any progress, the
fo
_ r_ c_e_s_ applied by each
team must be balanced.
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Examples of balanced forces
Before skydivers open their
parachute they fall with a constant
speed called their t e
_ r_ m
_ i_n_a_l _
velocity. This is because their
weight is balanced by the
a i_r_ r e
a n_ c_e_ _ on their
_ s_ i_s _t _
body.
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Air Resistance
Weight
18
Examples of balanced forces
When they open their parachute
they still fall at a constant speed
but much slower than before
because the air resistance is
r e_ a_ t_e_r_ with the parachute
g_
open.
q u_ a_l _
The air resistance is still e _
to the weight so the forces are still
balanced.
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Air Resistance
Weight
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Examples of balanced forces
Upward Force
Weight
When a plane is travelling
forwards, the air rushing over
the wings creates an
u_
pw
a r_ d_ force.
__
When the plane is flying level,
this upward force balances the
e i_g_h_t _ of the plane.
w_
When the plane is taking off and landing, the
upward and downward forces are n o_ t_ balanced.
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Intermediate 1
Physics
Movement
Speed and
acceleration

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Measuring average speed
We can measure the average speed of any object by
i s_t_a _n _c _
e _ it travels and the t i_m_ e_
measuring the d _
it takes to travel that distance.
Average speeds are usually measured over l a
_ r_ g_e_
o n_ g_ times.
distances or l _
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Measuring average speed
The average speed can then be found using the following
equation:
metres (m)
Average speed =
metres per second (m/s)
distance
time
seconds (s)
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Measuring average speed
The distance can be measured using a tape or m e_ t_r_e_
stick.
Time is measured by a s _
t o_ p_w_a_t_c_h _ or sometimes by
a timer which starts and stops automatically.
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Measuring average speed
Automatic timers are often
operated by light g a_ t_e_s_ .
When a moving object cuts
the beam of light gate 1, the
timer s t_ a_r_t_s _ timing.
1 246
Ti mer
li ght
gate 1
li ght
gate 2
When the moving object cuts the beam of light gate 2,
the timer s t_ o_p_s_ timing.
In this case,
the average speed =
distance between gates
time on timer
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Examples on calculating speed
1.
A car travels a distance of 45 m in 30 s.
Calculate its average speed.
Average speed =
=
distance
time
45
30
= 1.5 m/s
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Examples on calculating speed
2. A trolley passes through two light gates which are
2.5 metres apart.

The timer measures a time of 15 seconds.
What is the average speed of the trolley?
Average speed =
=
distance
time
2.5
15
= 0.167 m/s
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Examples on calculating speed
3. A trolley passes through two light gates which are
1.2 metres apart.
The timer measures a time of 0.8 seconds.
What is the average speed of the trolley?
Average speed =
=
distance
time
1.2
0.8
= 1.5 m/s
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Instantaneous Speed
Your speed at any particular point during a journey is
called the instantaneous speed - the speed at an instant.
Calculating this speed is the same as calculating the
l l _.
average speed but the time interval must be very s m
_ _a _
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Measuring Instantaneous Speed
To Supply
Card
Li ght gate
Millisecond Timer
0. 46
Trolley
Because the time to be measured is so small, there is a
o_
n _ time (the time taken by a
problem with r e
_ a_ c_t_i _
person to start and stop a timer).
To measure the speed of a moving trolley, it is better to
use a l _
i g_h_t_ g a_ t_e_ because there is no reaction time.
The trolley is fitted with a card. The timer measures the
t i_m_ e_ the card cuts off the beam of light.
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Measuring Instantaneous Speed
To Supply
Card
Li ght gate
Millisecond Timer
0. 46
Trolley
It s _
t a_ r_t_s_ when the card cuts the light gate beam and
it stops again when the beam is remade.
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Measuring Instantaneous Speed
To Supply
Li ght gate
Card
Millisecond Timer
0. 46
Trolley
The instantaneous speed is calculated using the length of
i s_t_a _n _
ce
card as the d _
_ _ and the timer reading as the
time, i.e.
metres (m)
Instantaneous speed =
length of card
time on timer
metres per second (m/s)
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seconds (s)
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Example on instantaneous speed
A trolley is fitted with a card 0.10 m in length. The trolley
is set in motion and the card cuts a light gate. The time on
the timer is 0.025 seconds. Calculate the speed of the
trolley when it passes the light gate.
Instantaneous speed =
length of card
time on timer
=
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0.10
0.025
= 4.0 m/s
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Acceleration
Acceleration is the change of speed of an object in
e c_ o_ n_d_ .
one s _
a s_ t_e_r_ , it is accelerating –
If an object is getting f _
the speed of the object is increasing.
l o_w_e_r_ , it is decelerating –
If an object is getting s _
the speed of the object is decreasing.
Do not confuse acceleration with speed.
i g_h_ speed but have zero
A car can be travelling at a h _
acceleration; also a car can have a high acceleration but
be travelling at a low s p_ e_ e_d_
(though its speed will not stay low for long!).
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Car performance
Car manufacturers often state a value for their car's
acceleration to indicate its performance.
The usual performance figure quoted is the t i_m_ e_ in
seconds it takes for the car to increase its speed from
rest to 60 mph.
A high performance car might be
quoted as: 0-60 mph in 5.0 s
i g_h_e_r _ the acceleration
The smaller the time, the h _
and the higher the performance.
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Car performance
The table below shows performance figures for some makes of car.
Make of Car
Mini
Increase
in Speed
0—> 60 mph
Time for increase
Volvo
0—> 60 mph
19.6 seconds
Ford
0—> 60 mph
8.1 seconds
Jaguar
0—> 60 mph
6.1 seconds
10.5 seconds
Questions:
a. Which car has the greatest acceleration?
Explain your answer.
b. Which car has the smallest acceleration?
Explain your answer.
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Car performance
The table below shows performance figures for some makes of car.
Make of Car
Mini
Increase
in Speed
0—> 60 mph
Time for increase
Volvo
0—> 60 mph
19.6 seconds
Ford
0—> 60 mph
8.1 seconds
Jaguar
0—> 60 mph
6.1 seconds
10.5 seconds
Answers:
a. The car with the greatest acceleration is the Jaguar
because it has the shortest time to make the same
increase in speed as all the others.
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Car performance
The table below shows performance figures for some makes of car.
Make of Car
Mini
Increase
in Speed
0—> 60 mph
Time for increase
Volvo
0—> 60 mph
19.6 seconds
Ford
0—> 60 mph
8.1 seconds
Jaguar
0—> 60 mph
6.1 seconds
10.5 seconds
Answers:
b. The car with the smallest acceleration is the Mini
because it has the longest time to make the same
increase in speed as all the others.
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Intermediate 1
Physics
Movement

Moving Bodies
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Collisions
MOVING BODIES
h a_ n_ g_e_d_ by another
When an object has its speed c _
object, we say the two objects collide.
Suppose object A is moving and collides with object B.
A
B
The effect of the collision is to change the speeds of
bo
_ t_ h_ the colliding objects.
The change in speed of the colliding objects is greater
when:
a) the objects are moving f a_ s_t_e_r_ before collision
b) the objects have a larger m a_ s_s_ .
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Change in speed
When an object has its speed changed, we say it has
been acted on by a f o
_ r_c_e_ .
(Forces occur during collisions).
r e_ a_t_e_r _ the change in the
The larger the force the g _
speed.
The longer the time a force is applied the greater is the
ch
_ a_ n_ g_e_ of speed.
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The range of a ball
When an object is thrown or fired, it travels a distance
horizontally before hitting the ground.
Eventually even the fastest thrown or fired object hits
the ground due to the force of g r_ a_v_i _t y_ _ pulling it
down.
This horizontal distance travelled is called the r a_ n_ g_e_ ,
i.e.
range
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The range of a ball
The range of a ball thrown or hit is changed by:
p e_ e_ d_ the ball is thrown or hit
a) the s _
(the f a
_ s_ t_e_r_ the speed the greater the range)
b) the a n
_ g_ l_e_ at which the ball is thrown or hit.
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The range of a ball
r a_ n_ g_e_ ) a golf
The distance (r
ball travels depends on the
speed of the club and the loft
an
(a
_ g_ l_e_ ) of the club.
The driver is designed to give
the greatest speed at the best
angle for maximum
d i_s_t_a _n _
ce
__.
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Height of rebound
Whenever a ball bounces, it l o_ s_e_s_ some of its energy
e i_g_h_t _ again.
so it never reaches the same h _
A ball dropped from a height of 80 cm might rebound to
height of 50 cm.
It will never rebound to a height of 80 cm.
When a ball hits a surface, it will rebound to a greater
height if:
a) its speed on impact is l a
_ r_g_e_
b) the surface it hits is h a_ r_d_ .
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Intermediate 1
Physics
Movement
End of Unit
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